Intuitive aptitude is the ability to understand the structure and operation of complex systems without special education or training. However, it also compels the holder to understand as much as they can, resulting in a "hunger" which can manifest a need to understand, which often causes Sylar to kill other evolved humans and acquire their abilities.

Limits

Sylar himself describes intuitive aptitude as the ability to understand how things work, and how to fix them if they are broken (Once Upon a Time in Texas). However, the latter aspect of the ability has almost never been utilized by Sylar after his abandonment of his former identity as Gabriel Gray, timepiece restorer.

Sylar's ability seems to be constantly active, unconsciously helping him to analyze any system that he encounters. For systems that he already understands (like watches), he can detect and identify flaws in the mechanism with only a cursory inspection. Systems that he has never seen before may require more extensive study, but he seems to be able to comprehend them far more quickly than any ordinary person could, and he requires far less technological equipment.

Sylar's ability seems to work for analyzing mechanical and biological systems. Whether it would work on other types of systems (such as electronic hardware or computer software) is not yet known, although he has claimed that it allows him to rapidly analyze human behavior (Fallout). The future versions of Peter and Sylar from the exposed future have both stated that intuitive apititude can even be used to understand the complexities of cause and effect (the "Butterfly Effect"), allowing one to control the course of the future (I Am Become Death). Sylar is also able to use his ability to understand the abilities of other evolved humans; while being attacked by Knox in the exposed future, Future Sylar immediately deduces that Knox draws his power from fear and states that Knox will be unable to fight him as he is not afraid (I Am Become Death).

With this ability, Sylar is able to study evolved humans to analyze their abilities and copy them, adding them to his own. He can also learn to control them more quickly than the original owners can (e.g. emitting multiple, controlled pulses of radiation from his hands soon after acquiring induced radioactivity).

Sylar does not need to kill someone to gain their ability. However, a physical study of the victim's brain requires direct observation necessitating the removal of the upper part of the skull, so the victim soon dies of blood loss and trauma. Victims with rapid cellular regeneration, however, can survive this by repairing the damage (The Second Coming). Sylar has demonstrated that can also "empathically" copy abilities without injuring the source, but still prefers the brain removal method out of a love of killing. He first demonstrated this by empathically copying electric manipulation from Elle. In order to do this, he had to connect with her by helping her to regain control of her powers. (It's Coming) Sylar later demonstrates this aspect of his ability on several occasions, copying shape shifting from James Martin (Into Asylum), flight from Nathan Petrelli (An Invisible Thread) , and empathy from Lydia during a romantic encounter with her. (Let It Bleed)

Angela explained to Sylar that his ability creates a hunger that can be controlled with structure. On the other hand, Arthur explained to Sylar that if he gained control of his emotions and helped someone else to deal with traumatizing personal emotions, he could gain a target's abilities without physical study of the brain, though with less control over the new ability (It's Coming). Both techniques have proved useful in allowing Sylar to control the hunger and gain abilities without having to kill his victims to study their brains. One of his future selves managed bring the hunger under control, fighting it every day for his son, Noah Gray.

Sylar can also detect some medical conditions, such as Charlie's aneurysm and Hiro's brain tumor. Perhaps due to his studies of the brain structure, he had enough knowledge about Charlie's aneurysm to remove it without hurting her. (Once Upon a Time in Texas)

Peter was exposed to this ability on Homecoming night, but needed a future Gabriel to explain how the ability works to access it. Gabriel gave Peter his broken watch to repair; performing the repair using telekinesis allowed Peter to manifest the ability. Afterward, Peter was able to understand Nathan's thought process and wanted to explore his thoughts more by slicing his head open, but stopped.

Future Gabriel also explained to Peter that the ability creates a hunger (i.e., an obsession to understand as much as possible) that is hard to control, and made him a killer. When Peter teleports to Sylar's Level 5 cell, Sylar notes that Peter now has the same hunger that Sylar has because of the ability. This hunger caused him to attack his own mother and start to slice her head open before Sylar stopped him.

Intuitive aptitude also seemed to help him gain better control over his previously absorbed powers: he was able to use telepathy on a stronger level than previously demonstrated, he could time travel and teleport much more accurately than in the past and his telekinesis was more refined than he had previously demonstrated.

Peter lost this ability after his father stole all of his powers from him.

As with Sylar, this ability caused Samson Gray to go on a killing spree to acquire abilities, including telekinesis and sedation, plus many others that he claims to have forgotten. Samson eventually gave up killing and seemed to suppress the hunger, but when he saw Sylar's regeneration at work, it caused the hunger to return. (Shades of Gray)

Examples

Gray (Sylar) detects a mechanical flaw in Chandra Suresh's wristwatch from across the room within moments of Chandra entering his shop. (Six Months Ago)

After seeing Brian Davis demonstrate his power of telekinesis, Sylar seems to "listen" to Davis's mind, indicating that he is able to "fix" Davis. Sylar then attacks and kills Davis. Shortly thereafter, Sylar is able to use telekinesis himself. (Six Months Ago)

Whilst visiting his mother, he notes that her clock is not working correctly and proceeds to fix it. (The Hard Part)

After removing the top of Claire's head, Sylar appears to understand the workings of her brain. He locates which part of the brain controls her power, and after examining it, seems to mentally alter himself. After doing so, he successfully imitates her ability by healing a knife wound. (The Second Coming)

Peter readsFuture Nathan's mind to tell if he's telling the truth, then determines that Nathan thinks he is doing the right thing, and is consumed by the hunger to see more of how Nathan's brain works. He attempts to open his skull in the same manner as Sylar but stops before completing it, killing Nathan.

After being punched by Knox, Sylar states that he understands Knox's power. (I Am Become Death)

Despite having Nathan's memory and mind, Sylar demonstrates this as he notices a clock is running fast and fixes it. (An Invisible Thread)

Even after losing all memory of his past, Sylar can tell that the clock on the wall of an interrogation room does not match Dr. Gibson's watch. She confirms her watch has been running fast. (Hysterical Blindness)

In the past, Sylar detects Charlie's blood clot and Hiro's brain tumor. After making a deal with Hiro, Sylar removes Charile's blood clot, which leaks through her eye (Once Upon a Time in Texas).

After an intimate encounter with Lydia, Sylar empathically gains her power of empathy. (Let It Bleed)

Memorable Quotes

"I can fix it."

"My watch isn't broken."

"Actually it is. Yeah, the self-winding coil is loose. Your watch is running two seconds slow."

"How did you know?"

"Just a talent I have for the way things work, how the parts should go."

"My ability is not just understanding how things work; there's a hunger that comes with it. To know more, to have more. I couldn't control it; it turned me into a killer, a monster. And every day is a struggle, every hour. But I fight it...for him. And I am not going to willingly condemn you to hell!"

Sylar typically learns to control stolen abilities far more quickly than the people from whom he acquired them. It is possible that his own intuitive aptitude helps him to rapidly analyze and assert control of new abilities.

Noah says to Elle that Sylar has the ability to "transfer power from one vessel to another" (Villains). Noah is technically incorrect, as Sylar is actually copying the power, not transferring it. (The Second Coming)

Samson Gray, who possesses this ability, attempted to open Sylar's head to obtain Sylar's regeneration, suggesting that one person with this ability can gain all the acquired abilities of another with the same power.

Ironically, this ability is not intuitive to those who absorb it. Peter Petrelli could not access it due to its complexity before consulting a future Gabriel Gray on its use.

The "hunger" portion of intuitive aptitude is apparently immune to the Shanti virus; Sylar still felt it during his infection, even though he couldn't obtain or use any of his abilities.

Arthur Petrellistole his son Peter's abilities, saying, "I have [your powers] now." It is presumed that Arthur stole all of Peter's abilities, including intuitive aptitude. However, it is possible that Arthur did not steal all of Peter's abilities. Since Arthur never used this ability, there is no conclusive evidence that he actually stole this ability.

Trivia

Sylar's dossier describes his intuitive aptitude as "his intuitive understanding of the biological workings of individuals."